This invention relates a high density dial router and more particularly to a Fault Tolerant Dial Router (FTDR) that can be automatically reconfigured around faults while other independently operating subsystems in the dial router continue to process calls.
A dial router processes telephone calls from a Public Service Telephone Network (PSTN). The dial router formats received telephone calls into IP packets and routs the packets over a packet-based Local Area Network (LAN) or Wide Area Network (WAN). The PSTN serially multiplexes multiple telephone calls together into either PRI, channelized T1 (CT1), or channelized T3 (CT3) data streams or the European equivalent of CT1, which are referred to as CE1. The dial router accordingly includes PR1, CT1, CE1 and/or CT3 feature boards that separate out the individual calls from the data streams. Modems extract digital data from the individual telephone line channels. The router then encapsulates the digital data into packets that are routed onto the packet-based network, such as a fast-Ethernet LAN.
Some dial router architectures break the dial router system into many very small subsystems cards. Each subsystem has a complete set of line interface units. When a failure occurs, the whole subsystem card is decommissioned and manually swapped by an operator with a standby subsystem card at a later time. Even if a line interface unit is partially operational, it is fully decommissioned if a failure is detected. Another problem is that the number of boards in the dial router is substantially increased since one redundant card is provided for each subsystem card. This redundant architecture results in large and bulky dial routers.
Current dial routers provide little or no fault tolerance against failures that occur in the field. Upon encountering a failure, field service engineers typically swap out the entire dial router box. For example, when a single modem module in the dial router fails, the entire dial router box is turned off and the modem card replaced. When the dial router is shut down, all calls coming into the dial router are disrupted. Because the dial router handles a large number of calls at the same time, any failure, no matter how small, disrupts all the information (data, voice, etc.).
Accordingly, a need remains for a simple dial router architecture that reduces the disruption of calls caused by failures.